Master cylinders are in wide use in various industries, but particularly in the motor vehicle industry where they serve in conjunction with an associated slave or wheel brake cylinder located at each of the wheels of the vehicle. Each wheel brake cylinder is supplied with pressurized fluid when an operator depressing the brake pedal of the vehicle actuates the master cylinder. Although manual actuation of the master cylinder can be effective to produce the desired resultant action at the associated brake cylinder, often it is desirable to provide power-assist operation of the master cylinder.
Many current brake systems include such a power-assist feature using engine vacuum to boost the operation of the master cylinder. In a system where engine vacuum is not available, such as in an electric-powered vehicle, it would be desirable to provide a brake boost feature that provides similar functionality as that of vacuum or other boost schemes. Some boosters have provided a master cylinder having a non-vacuum boost feature in combination with a manual actuation feature in order to ensure continuous operation of the brake system in the event the boost feature becomes disabled. These boosters utilize a linearly translated ball screw to engage with the master cylinder. A ball nut rotates and transmits power from a driven pulley to the ball screw. The ball nut is supported by a ball nut bearing. This arrangement requires a very large bearing over the ball nut, and the bearing diameter and motor diameter force a further center to center distance of ball screw and motor, resulting in large overall packaging of the booster.
It is desirable to provide a power assist system with a ball nut and ball screw arrangement that provides a smaller package that is more cost effective and less noisy than conventional power assist systems.